We could all do to be a little more hydrated, but there's truth in the phrase "too much of a good thing". You can definitely have too much water, and we're not just talking about drowning. Water intoxication, caused by the massive over-consumption of water (either for a competition, during sport or as a result of dropping too much E), basically sends your electrolyte balances haywire, causing a disturbance of brain function. Any high school student knows that water enters cells by osmosis. When you consume massive amounts of water, the fluid outside of the cell has significantly lower electrolyte (i.e. salt) levels than inside, so it starts shifting through, causing the cells to swell. This is bad news, particularly if those swelling cells happen to be the one sin your brain. As the brain swells, it puts it under a load of pressure. This will cause headache, drowsiness and disorientation. If pressure builds up in the brain stem, it can shut off the central nervous system as well as cutting off blood circulation, leading to cerebral edema. This, suffice to say, is seriously unpleasant, leading to seizures, brain damage, coma or death.
